Rod lock for ram blowout preventers

ABSTRACT

A blowout preventer to hydraulically seal a wellbore includes a housing configured to be positioned above a wellhead and to surround a drillstring, a plurality of rams positioned perpendicular to an axis of the drillstring to engage the drillstring and hydraulically isolate an annulus between the wellbore and the drillstring when in a closed position, and a roller lock positioned about a thrust rod of each ram configured to maintain the rams in the closed position.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates generally to locking mechanisms for a blowout preventer as deployed in the petroleum exploration and recovery industry. More particularly, the invention relates to a roller lock mechanism to prevent the undesirable reversal of a thrust rod for a ram-type blowout preventer.

2. Background Art

Wellbores are drilled deep into the earth's crust to recover oil and gas deposits trapped in the formations below. Typically, these wellbores are drilled by an apparatus that rotates a drill bit at the end of a long collection, or string, of threaded pipes known as a drillstring. Because of the energy and friction involved in such an operation, a drilling fluid, commonly referred to as drilling mud, is used to lubricate and cool the drill bit as it cuts the rock formations below. Furthermore, the drilling mud is capable of performing the secondary function of removing the drill cuttings from the bottom of the wellbore to the surface. Typically, drilling mud is delivered to the drill bit under high pressures through a central bore of the drillstring. From there, nozzles on the drill bit direct the pressurized mud to the cutters on the drill bit where the pressurized mud cleans and cools the bit. As the fluid is delivered downhole through the central bore of the drillstring, the fluid returns to the surface in the annulus formed between the outside of the drillstring components and the cut wellbore. Therefore, a hydrostatic column of drilling mud typically extends from the surface to the bottom of the hole being cut.

As wellbores are drilled several thousand feet below the surface, the hydrostatic column of drilling mud serves to help prevent blowout of the wellbore as well. Often, hydrocarbons and other fluids trapped in subterranean formations exist under significant pressures. Absent any flow control schemes, fluids from such ruptured formations can blow out of the wellbore like a geyser and spew hydrocarbons and other undesirable fluids into the atmosphere. Several thousand feet of hydraulic head from the drilling mud column helps to prevent the wellbore from blowing out under normal conditions. However, under certain unforeseen circumstances, the drill bit will encounter pockets of pressurized formations and will cause the wellbore to “kick” or experience a rapid increase in pressure. Because formation kicks are unpredictable and would otherwise result in disaster, flow control devices known as blowout preventers (“BOP's”), are mandatory on most drilling rigs in use today.

Blowout preventers are devices configured to seal the annular space that surrounds the drillstring. One of the most common types of blowout preventer is known as a ram-type blowout preventer. A ram-type blowout preventer includes a large housing mounted atop the wellhead that includes a large passageway through which the drillstring (and any components connected thereto) is able to pass. The housing also includes two or more rams located in a plane substantially normal to the axis of the drillstring and wellhead that are configured to move between retracted and extended positions. The ends of the rams are configured so that when extended, they provide a complete annular hydraulic seal around the drillstring disposed therethrough.

Referring initially to FIG. 1, a typical ram-type BOP 100 is shown schematically. Ram-type BOP 100 shown includes a main housing 102, two or more piston ram housings 104, and top 106 and bottom 108 bolting flanges for connection to other wellhead components (not shown). Ram-type blowout preventer 100 is preferably constructed such that a generally cylindrical through bore 110 allows oilfield tubulars 112 to unobstructedly pass through along a drillstring axis 114. Oilfield tubulars 112 are typically components of a drillstring and may include, but are not limited to, drill pipe, drill collars, measurement tools, coiled tubing, or wirelines. Under normal conditions, through bore 110 is open and not obstructed such that fluids pass through an annulus 116 formed between the outer profile of tubulars 112 and the inner profile of through bore 110. When the wellbore below is to be shut off such that fluids below BOP 100 can no longer communicate with the wellbore above BOP 100, ram assemblies 118 are activated to provide a 360° seal of annulus 116 between bore 110 and tubulars 112.

Each ram assembly 118 includes a sealing ram 120 having a leading edge 122 connected to a hydraulic piston 124 through a thrust rod 126. Leading edge 122 is preferably contoured such that it corresponds with an outer profile of oilfield tubular 112 so that a tight seal can be formed therebetween. Connected to sealing rams 120 through thrust rods 126, hydraulic pistons are activated by an external hydraulic source (not shown) to engage leading edges 122 against tubular 112 and seal off annulus 116. While it may be typical for there to be two ram assemblies 118, each with a corresponding semi-circular profile for leading edges 122, it should be understood that a ram-type BOP 100 may employ three or more ram assemblies 118 with corresponding circular portions for leading edges 122 to shut off and seal annulus 116.

To seal off annulus 116, pressurized fluids are applied to hydraulic port 128 in communication with a reservoir 130 of ram housing 104. Increases in pressure in reservoir 130 urge back face 132 of piston 124, causing piston 124, rod, 126, and ram 120 to be thrust toward tubular 112. The higher the pressure in communication with reservoir 130, the higher the loads transmitted through rod 126 to ram 120. To retract rams 120 out of annulus 116, pressure to port 128 is reduced and piston 124 is able to retract into reservoir 130. Retraction of pistons 124 may be assisted through the use of retraction springs (not shown), hydraulic retraction, or through any other means known in the art. Particularly, a retraction port 129 can be used to provide hydraulic access to a retraction reservoir 131, such that an increase in hydraulic pressure displaces piston 124 to retract ram 120.

With rams 120 extended and leading edges 122 engaging oilfield tubular 112, a strong hydraulic seal prevents fluid from escaping the wellbore through annulus 116. As long as hydraulic pressure is maintained in reservoir 130, rams 120 will continue to seal annulus 116. However, there are circumstances where it is desired to maintain the annular seal regardless of the operational abilities of ram-type BOP 100. For example, it is desirable to maintain seal integrity in the event of a power failure at the rigsite. Furthermore, if wellbore is to be shut-in for an extended period of time, maintaining hydraulic pressure over that time period is not always reliable or prudent. Therefore, systems and mechanisms to “lock” hydraulic rams 120 in place once activated are highly desirable in the oilfield.

One former method to lock hydraulic rams 120 in place involves the tightening of mechanical screws to lock pistons 124 in place once displaced in reservoir 130. Such screws were tightened either manually or through power devices and would effectively lock rams 120, thrust rods 126, and pistons 124 in place. However, accessibility concerns make such a solution less than optimal. Particularly, in deep-sea installations, these locking screws must be activated by remotely operated vehicles or through electrical actuators. As such, their reliability is suspect in depths of several hundred feet or more. Furthermore, on land-based rigs, the BOP 100 is typically located beneath the rig floor. As such, engaging and disengaging the locking screws takes considerable time, time that is not always available in the event of an emergency.

Additional solutions to lock hydraulic rams are available to lock thrust rods 126 in place. Formerly, ratchet profiles (e.g. U.S. Pat. No. 3,941,141 to Robert, hereby incorporated by reference herein) have been used upon the outer profiles of thrust rods 126 in conjunction with matching locking members to retain thrust rods 126 in place. Furthermore, various internal threaded mechanisms (e.g U.S. Pat. No. 4,052,995 to Ellison and U.S. Pat. No. 4,076,208 to Olson, both hereby incorporated by reference herein) have been employed to secure thrust rods 126 in place using whereby thrust rods 126 are threaded and corresponding jam-nut devices lock thrust rods 126 in place. Finally, various wedging solutions (e.g. U.S. Pat. Nos. 4,305,565 to Abbe and U.S. Pat. No. 4,969,390 to Williams, both hereby incorporated by reference herein) have been proposed to lock thrust rods 126 in place. While promising, each of these solutions are considered by many to be less than optimal in that they exhibit a slight amount of slip or “play” in the reverse direction known as backlash before they engage and lock the thrust rods 126 in place. In the event of a high pressure “kick” to a wellbore, even infinitesimal displacements in rams 120 connected to thrust rods 126 can result in a catastrophic release of wellbore fluids.

Therefore, there is a long-felt need in the industry for an apparatus to quickly, positively, and solidly lock ram-type blowout preventers in an engaged position with minimal operator interaction and with minimal backlash of the rams before locking occurs.

SUMMARY OF INVENTION

In one embodiment, a blowout preventer includes a housing configured to be positioned above a wellhead and to surround a drillstring, a plurality of rams positioned perpendicular to an axis of the drillstring, and a roller lock positioned about a thrust rod of each ram. The rams may be configured to engage the drillstring and hydraulically isolate an annulus between the wellbore and the drillstring from components located above the housing when the rams are in a closed position. The roller locks may be configured to maintain the rams in the closed position.

In one aspect, the present invention related to a locking apparatus to be used with a blowout preventer. In one embodiment, the locking apparatus includes a plurality of spherical locking elements to engage and restrict movement of thrust rods connected to rams of the blowout preventer. The locking apparatus may also include a plurality of receptacles for the spherical locking elements, wherein each receptacle includes an inclined surface configured to thrust the spherical locking elements into compressive contact with the thrust rods when the operating rams are urged open. Furthermore, the locking apparatus may also include a release cage to retract and retain the spherical locking elements into the receptacles and to direct them out of compressive contact with the thrust rods when the operating rams are to be opened.

In one aspect, the present invention relates to a method to lock rams of a blowout preventer. The method may include positioning spherical locking elements inside receptacles located adjacent to thrust rods of the rams, wherein the receptacles include inclined surfaces configured to engage the spherical locking elements into the thrust rods when the rams are urged open. The method may further include locking the thrust rods with compressive engagement of the spherical locking elements. The method may further include retracting the spherical locking elements into their respective receptacles with a release cage to unlock the rams.

Other aspects and advantages of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic section-view drawing of a ram-type blowout preventer.

FIG. 2 is a schematic drawing of a thrust rod retainer in accordance with an embodiment of the present invention.

FIG. 3 is a schematic drawing of a thrust rod retainer in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Referring now to FIG. 2, a schematic representation of a thrust rod lock 250 in accordance with an embodiment of the present invention is shown. In this embodiment, thrust rod lock 250 is preferably located within a piston ram housing (e.g. 104 of FIG. 1) in a fixed position surrounding a thrust rod 226. Thrust rod lock 250 is desirably configured to allow displacement of thrust rod 226 in a locking direction 252, while disallowing displacement of thrust rod 226 in an unlocking direction 254. Thrust rod lock 250 includes a main body 256, into which one or more roller receptacles 258 are formed. Roller receptacle 258 is shown including a deep section 260 that extends to a shallow section 262 through an inclined surface 264.

As such, each roller receptacle 258 is configured to retain and deploy a roller 266 within and from receptacle 258 when locking of thrust rod 226 is selectively desired. Particularly, when roller 266 is located within deep section 260, substantially no contact occurs between roller and thrust rod 226, but as roller 266 travels down inclined surface 264, thrust rod 226 is increasingly locked into a bind by roller 266 and surface 264. Furthermore, once so locked, further increases in load upon thrust rod 226 in unlocking direction 254 tend to cause roller 266 in contact with inclined surface 264 to compress against thrust rod 226 even tighter, resulting in an even stronger locked position. Displacements of thrust rod 226 in locking direction 252 tend to roll roller 266 up inclined surface 264 toward deep section 260 of main body 256, such that rod 226 is free to move in locking direction 252.

Furthermore, a retainer cage 268 of thrust rod lock 250 retains roller 266 within receptacle 258 and is configured to retrieve roller 266 into deep section 260 when thrust rod 226 is to be released. Retainer cage 268 preferably includes a slot (not shown) adjacent to roller 266 to allow retainer cage 268 to displace roller 266 without interfering with the roller's engagement with thrust rod 226. In the case where roller 266 is a spherical roller, slot can be a longitudinal slot or a spherical section to match the outer profile of roller 266. Alternatively, in the case where roller 266 is cylindrical, the slot can be a transverse slot approximately the same width as roller 266. Regardless of configuration, when thrust rod 226 is to be displaced in unlocking direction 254, retainer cage 268 is displaced in direction 270 to retrieve roller 266 up inclined surface 264 and into deep section 260, away from the engagement with outer surface of thrust rod 226. Retainer cage 268 may be biased so that roller 266 is biased in the direction opposite 270 and into thrust rod 226. Alternatively, cage 268 may be unbiased allowing movement of thrust rod 226 to be the sole force in causing roller 266 to be engaged therewith.

It should be understood that any means to displace or bias retainer cage known in the art may be employed, including, but not limited to, hydraulic lines, springs, and tension cables. Particularly, retainer cage can be constructed to be displaced when hydraulic pressure is applied to a hydraulic actuator attached thereto. Furthermore, if a hydraulic device is employed to retract thrust rod 226 into unlocking direction 254, a control system (not shown) can be used to direct such hydraulic pressure to either the retainer cage actuator, the thrust rod retractor, or both. Alternatively, a hydraulic system to release thrust rod lock 250 can be distinct from a hydraulic system to displace thrust rod 226 in unlocking direction 254.

Furthermore, it should be understood that inclined surface 264 can be any of various types known in the art. Particularly, surface 264 can be a mere planar surface or can be profiled to fit the contours of spherical rollers 266. Furthermore, while rollers 266 are described generically, it should be understood that they can be constructed as spherical or cylindrical devices and can be constructed with various hardness and friction values to facilitate contact and engagement between thrust rod 226 and inclined surface 264.

Referring now to FIG. 3, a schematic of a thrust rod lock 350 in accordance with an embodiment of the present invention is shown. Like thrust rod lock 250 of FIG. 2, thrust rod lock 350 of FIG. 3 is preferably located within a piston ram housing 304 in a fixed position surrounding a thrust rod 326. While a single thrust rod lock 350 is shown, it should be understood that a plurality of rod locks 350 can surround thrust rod 326 radially and axially.

Thrust rod lock 350 is desirably configured to allow displacement of a thrust rod 326 in a locking direction 352, while resisting displacement of thrust rod 326 in an unlocking direction 354. Thrust rod lock 350 includes a main body 356, into which two series of roller receptacles 358A, 358B are formed. Like receptacles 258 of FIG. 2, inner roller receptacle 358A is profiled to urge a roller 366A into engagement with thrust rod 326 when thrust rod 326 is displaced in unlocking direction 354. At the same time, outer roller receptacle 358B is profiled to urge a roller 366B into engagement with an outer wear plate 380 when main body 356 is displaced in unlocking direction 354. Therefore, for each location about and along thrust rod 326, one roller 366A bites with thrust rod 326 and another roller 366B bites with wear plate 380 to resist displacement of thrust rod 326 in unlocking direction 354. As such, for each incremental displacement in unlocking direction 354, thrust rod 326 of FIG. 3 will experience double the radial compression as would be experienced by a thrust rod in a single roller configuration (e.g. FIG. 2).

Furthermore, inner and outer retainer cages 368A, 368B retain rollers 366A, 366B inside receptacles 358A, 358B and allow for rod lock 350 to be released once retraction of thrust rod 326 is desired. As with retainer cage 268 of FIG. 2, retainer cages 368A, 368B allow rollers 366A, 366B to contact thrust rod 326 and wear place 380 through slots or other forms of apertures (not shown) therethrough. As before, such apertures in retainer cages 368A, 368B can take the form of longitudinal slots or spherical sections in the case where rollers 366A, 366B are spherical or can be transverse slots if rollers 366A, 366B are cylindrical. A pair of bias springs 382, 384 is shown working in conjunction with main body 356 and retainer cages 368A, 368B to thrust rollers 366A, 366B into locking engagement with thrust rod 326 and wear plate 380 by default. As inner retainer cage 368A is fixed relative to housing 304, spring 382 urges main body in the direction of arrow 352 such that inclined surface 364A urges roller 366A into contact with thrust rod 326. Likewise, spring 384 between main body 356 and outer retainer cage 368B urges cage 368B and roller 366B in the direction of arrow 352 such that inclined surface 364B urges roller 366B into contact with wear plate 380.

To release rollers 366A, 366B from their engagement with thrust rod 326 and wear plate 380, an unlocking mechanism 386 is employed. Unlocking mechanism 386 can be constructed any number of ways, but is preferably configured to retract rollers 366A, 366B into their respective receptacles 358A, 358B so that thrust rod 326 can be retracted in unlocking direction 354. Unlocking mechanism 386 of FIG. 3 is shown within a recess 388 of housing 304. A hydraulic seal 390 surrounding mechanism 386 ensures that when hydraulic pressure is increased to a hydraulic port 392, mechanism 386 is displaced in the direction of 354 such that a thrust face 394 engages a corresponding load shoulder 396 of outer retainer cage 368B. When pressure to port 392 is sufficiently elevated, springs 384 and 382 are compressed such that rollers 366A, 366B are retained within recesses 358A, 358B to enable thrust rod 326 to be retracted. Once thrust rod 326 is retracted, pressure to port 392 can be released so that thrust rod 326 can be quickly engaged and held in place without any secondary locking step necessary. In its ordinary, equilibrium state, rod lock assembly 350 resists disengagement of thrust rod 326 without any supplemental steps, even in the event of total loss of hydraulic power.

Rod lock assemblies 250 and 350 of the present invention exhibit many advantages over locking mechanisms currently available. In particular, rod lock assemblies 250, 350 are capable of securing thrust rods 226, 326 almost instantaneously and with little or no backlash or slippage. Furthermore, rod lock assemblies 250, 350 are disclosed as “fail safe” devices, in that they lock by default. No affirmative steps are necessary to lock thrust rods 226, 326 in place once they are extended. Rod lock assemblies 250, 350 automatically engage and resist disengagement of thrust rods 226, 326. As no external power source is necessary to engage rod locks 250, 350, their effectiveness is not compromised by power failures. In contrast, hydraulic (or other) power is only necessary to disengage rod locks 250, 350. Finally, as rod locks 250, 350 are configured to engage smooth outer profiles of thrust rods 226, 326, no obstructive features are necessary on thrust rods 226, 326. Former solutions required special profiles that could obstruct thrust rod 226, 326 operation and engagement.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims. 

1. A blowout preventer to hydraulically seal a wellbore, comprising: a housing configured to be positioned above a wellhead and to surround a drillstring; a plurality of rams positioned perpendicular to an axis of the drillstring, the rams configured to engage the drillstring and hydraulically isolate an annulus between the wellbore and the drillstring from components located above the housing when the rams are a closed position; and a roller lock positioned about a thrust rod of each ram, the roller locks configured to maintain the rams in the closed position.
 2. The blowout preventer of claim 1, wherein the roller lock includes a plurality of spherical rollers in contact with inclined surfaces, the inclined surfaces configured to thrust the spherical rollers into compressive engagement with the thrust rods when the rams are displaced away from the drillstring.
 3. The blowout preventer of claim 2, wherein the spherical rollers and the inclined surfaces allow movement of the rams into engagement with the drillstring.
 4. The blowout preventer of claim 2, wherein the roller lock includes a release cage configured to retrieve the spherical rollers out of compressive engagement with the thrust rods to allow movement of the rams out of the closed position.
 5. The blowout preventer of claim 4, wherein the release cage is also configured to retain the spherical rollers within contoured pockets containing the inclined surfaces.
 6. The blowout preventer of claim 2, wherein the inclined surfaces comprise planar surfaces.
 7. The blowout preventer of claim 2, wherein the inclined surfaces comprise contoured surfaces.
 8. The blowout preventer of claim 1, wherein the roller lock comprises a plurality of cylindrical rollers in contact with inclined planes, the inclined planes configured to thrust the cylindrical rollers into compressive engagement with the thrust rods when the rams are displaced away from the drillstring.
 9. The blowout preventer of claim 1, wherein the roller lock includes a release mechanism to allow the rams to be displaced from the closed position.
 10. The blowout preventer of claim 1, wherein the roller lock includes a release mechanism actuated when hydraulic pressure is applied to retract the piston.
 11. A locking apparatus to be used with a blowout preventer comprising: a plurality of spherical locking elements to engage and restrict movement of thrust rods connected to rams of the blowout preventer; a plurality of receptacles for the spherical locking elements, each receptacle including an inclined surface configured to thrust the spherical locking elements into compressive contact with the thrust rods when the operating rams are urged open; and a release cage to retract and retain the spherical locking elements into the receptacles and to direct them out of compressive contact with the thrust rods when the operating rams are to be opened.
 12. The locking apparatus of claim 11, wherein the spherical locking elements permit movement of the operating rams in a direction of closure when in contact with the thrust rods.
 13. The locking apparatus of claim 11, wherein the inclined surfaces of the receptacles are planar surfaces.
 14. The locking apparatus of claim 11, wherein the inclined surfaces of the receptacles are contoured surfaces.
 15. The locking apparatus of claim 14, wherein the contoured surfaces correspond to the spherical locking elements.
 16. The locking apparatus of claim 11, wherein the receptacles include pockets into which the spherical locking elements can be fully retracted away from the thrust rods.
 17. The locking apparatus of claim 11, wherein the release cage prevents the loss of the spherical locking elements when no tubular objects extend through the blowout preventer.
 18. A method to lock rams of a blowout preventer, comprising: positioning spherical locking elements inside receptacles located adjacent to thrust rods of the rams, wherein the receptacles include inclined surfaces configured to engage the spherical locking elements into the thrust rods when the rams are urged open; locking the thrust rods with compressive engagement of the spherical locking elements therewith; and retracting the spherical locking elements into their respective receptacles with a release cage to unlock the rams.
 19. The method of claim 18, further comprising: retaining the spherical locking elements in the receptacles with the release cage, wherein the release cage includes apertures to allow the spherical locking elements to contact the thrust rods without falling out of the receptacles.
 20. The method of claim 18, wherein the release cage is a single component configured to retract all the spherical locking elements into their respective receptacles.
 21. The method of claim 18, wherein the release cage is comprised of a plurality of components, each configured to retract one or more spherical locking elements into their respective receptacles. 